Authors’ reply

to maintain systemic vascular resistance, to decrease on its pharmacological profile and the physiology of TOF, halothane may be a better selection, particularly in those pulmonary vascular resistance and to avoid myocardial predisposed to cyanotic spells and in the very young. In depression’. caring for patients with TOF, we routinely use sevoflurane While induction with halothane is generally well for induction and then switch to halothane for maintenance. tolerated by children with TOF, the more rapid induction This strategy not only appears to reduce the frequency and with sevoflurane in oxygen instead of halothane in oxygen degree of shunting, but also makes treating the episode much or halothane/nitrous oxide in oxygen would seem to faster and easier with phenylephrine, fluid, and deepening of provide a greater margin of safety until the airway can be the anaesthetic plane. secured (2). However, the use of halothane has potentially DOUGLAS G. RIRIE significant physiological benefits in management of JAMES J. O’BRIEN children with TOF once the airway is secure. Department of Anesthesiology While myocardial depression is not a goal in the Wake Forest University School of Medicine anaesthetic management of TOF, some element of Medical Center Boulevard decreased myocardial contractility or negative inotropy Winston-Salem, NC 27157-1009, USA may reduce the likelihood of right-to-left shunting by relaxing dynamic infundibular outflow tract obstruction. Halothane appears to be a more potent negative inotrope References than does sevoflurane in children and, therefore, may 1 Chiu CL, Wang CY. Sevoflurane for dental extraction in children provide greater relaxation of the dynamic obstruction at with Tetralogy of Fallot. Paed Anaesth 1999; 9: 268–270. the level of the infundibulum (3,4). 2 Black A, Sury MR, Hemington L et al. A comparison of the Another means of reducing outflow tract obstruction is induction characteristics of sevoflurane and halothane in to increase right ventricular volume. This may be children. Anaesthesia 1996; 51: 539–542. accomplished directly via intravenous administration of 3 Holzman RS, van der Velde ME, Kaus SJ et al. Sevoflurane fluid, or indirectly, by slowing the heart rate, thereby depresses myocardial contractility less than halothane during lengthening diastolic filling time and increasing ventricular induction of anesthesia in children. Anesthesiology 1996; 85: 1260–1267. end-diastolic volume. The fact that sevoflurane seems to 4 Wessel DL, Hickey PR. Anesthesia for congenital heart disease. maintain a higher heart rate than halothane may also make In: Gregory GA, ed. Pediatric Anesthesia. New York: Churchill sevoflurane a less desirable agent in patients with TOF; Livingstone, 1994; 501–503. faster heart rate may reduce ventricular filling time, 5 Sarner JB, Levine M, Davis PJ et al. Clinical characteristic of ventricular end-diastolic volume exacerbating right sevoflurane in children. A comparison with halothane. ventricular outflow tract obstruction (5). Anesthesiology 1995; 82: 38–46. Maintenance of systemic vascular resistance may be the 6 Ririe DG. Sevoflurane causes greater vascular relaxation of isolated aortic vessels of the rat than halothane [abstract]. most important factor determining right-to-left shunting in Anesthesiology 1998; 89(3A): A1326. these patients. High systemic vascular resistance promotes 7 Wodey E, Pladys P, Copin C et al. Comparative hemodynamic pulmonary blood flow, reducing net right-to-left shunting depression of sevoflurane versus halothane in infants: an and decreasing cyanosis. Halothane maintains vascular echocardiographic study. Anesthesiology 1997; 87: 795–800. tone better than sevoflurane and thereby provides for a 8 Ririe DG. Age-dependent effects of desflurane on relaxation of greater maintenance of systemic vascular resistance (6,7). vascular smooth muscle [abstract]. Anesthesiology 1998; 89(3A): The decrease in vascular tone from volatile anaesthetics is A1327. greater in the young and therefore sevoflurane’s effect on reducing systemic vascular resistance may make right-toleft shunting even worse in the very young with TOF (8). Authors’ reply Treatment of cyanotic spells can be accomplished Sir—Thank you for the opportunity to reply to the letter by increasing systemic vascular resistance with the from Drs Ririe and O’Brien. We are glad they found our administration of phenylephrine. With this in mind, paper interesting. However, we feel that Drs Ririe and sevoflurane also appears to shift the phenylephrine O’Brien have misinterpreted our paper. In our case report, response curve of the systemic vessels to the right when we described the use of sevoflurane in two children with compared to halothane (unpublished data from our Tetralogy of Fallot (TOF) presented for dental extraction. laboratory). This suggests that higher doses of Although sevoflurane may have some advantages over phenylephrine may be needed clinically for the same effect halothane in these children, especially the rapid and smooth on vascular tone in the presence of sevoflurane when induction and the earlier emergence, we never implied that compared to halothane. sevoflurane is the best choice for anaesthetic maintenance in In summary, while we have no fundamental problem with children with TOF. We merely concluded that sevoflurane the report by Chiu and Wang, we believe it is important to has some advantages over halothane in children with TOF understand that sevoflurane may not be the best choice for anaesthetic maintenance in children with TOF. In fact, based for dental extraction and therefore may be used in these


References
end-diastolic volume. The fact that sevoflurane seems to 4 Wessel DL, Hickey PR. Anesthesia for congenital heart disease. maintain a higher heart rate than halothane may also make In: Gregory GA, ed. Pediatric Anesthesia. New York: Churchill sevoflurane a less desirable agent in patients with TOF; Livingstone, 1994;501-503. faster heart rate may reduce ventricular filling time,  The decrease in vascular tone from volatile anaesthetics is A1327. greater in the young and therefore sevoflurane's effect on reducing systemic vascular resistance may make right-toleft shunting even worse in the very young with TOF (8).

Authors' reply
Treatment of cyanotic spells can be accomplished Sir-Thank you for the opportunity to reply to the letter by increasing systemic vascular resistance with the from Drs Ririe and O'Brien. We are glad they found our administration of phenylephrine. With this in mind, paper interesting. However, we feel that Drs Ririe and sevoflurane also appears to shift the phenylephrine O'Brien have misinterpreted our paper. In our case report, response curve of the systemic vessels to the right when we described the use of sevoflurane in two children with compared to halothane (unpublished data from our Tetralogy of Fallot (TOF) presented for dental extraction. laboratory). This suggests that higher doses of Although sevoflurane may have some advantages over phenylephrine may be needed clinically for the same effect halothane in these children, especially the rapid and smooth on vascular tone in the presence of sevoflurane when induction and the earlier emergence, we never implied that compared to halothane. sevoflurane is the best choice for anaesthetic maintenance in In summary, while we have no fundamental problem with children with TOF. We merely concluded that sevoflurane the report by Chiu and Wang, we believe it is important to has some advantages over halothane in children with TOF understand that sevoflurane may not be the best choice for anaesthetic maintenance in children with TOF. In fact, based for dental extraction and therefore may be used in these children. Obviously, further studies would need to be Finally, we feel that sevoflurane certainly provides better induction and recovery profile in children with TOF conducted to evaluate and compare its use with halothane in these children. Even then we believe it will still be undergoing dental extraction. Some, but not all, of its cardiovascular profile may be better than halothane. difficult to conclude that sevoflurane is the best choice in these children and vice versa.
However, it is obvious that in children with TOF an individualized anaesthetic management plan is essential Second, we do agree, in principle, with Ririe and O'Brien that some of the pharmacological profile of halothane may depending on the age, severity of the lesion, the type of the surgical procedure and the need for postoperative be beneficial in children with TOF. We agree with them that sevoflurane causes more reduction in systemic vascular ventilation. The choice of a particular anaesthetic agent based on sound pharmacological and physiological resistance and that this is not desirable. In our discussion, we cautioned that 'sevoflurane, despite causing lesser principles is less important than the skilled execution of the anaesthetic plan. decrease in cardiac output, does reduce the systemic vascular resistance and can potentially worsen intracardiac C.L. CHIU C.Y. WANG shunt'.
We were interested to hear that sevoflurane appeared to Department of Anaesthesia University of Malaya shift the phenylephrine response curve of the systemic vessels to the right compared with halothane. We are not Lembah Pantai 59100 Kuala Lumpur able to comment on this since phenylephrine is not available in our hospital, thus we have no experience in using it. Malaysia Erratum Figure 1 Some hints to make neonatal epidural Identification of the epidural space with microdrip infusion anaesthesia less difficult technique. A microdrip intravenous infusion set is connected to the epidural needle in place of a loss-of-resistance Yamashita M, Osaka Y. Some hints to make neonatal episyringe. This technique allows us to use both hands to dural anaesthesia less difficult. Paed Anaesth 2000; 10:114advance the needle, so a precise control of the needle 115.
advancement is easily accomplished. The correct legends to the figures for the above correspondence are reproduced below:

Figure 2
A manoeuvre to advance the catheter beyond the needle tip. (a) Both the epidural catheter and the introducer, which is withdrawn approximately 5 mm from the distal end of the hub, are pinched together by thumb and index finger. (b) Subsequently, both the introducer and the catheter are advanced together.